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1.
Microstructural Evolution and Solidification Behavior of Al-Mg-Si Alloy in High-Pressure Die Casting
Shouxun Ji Yun Wang D. Watson Z. Fan 《Metallurgical and Materials Transactions A》2013,44(7):3185-3197
Microstructural evolution and solidification behavior of Al-5 wt pct Mg-1.5 wt pct Si-0.6 wt pct Mn-0.2 wt pct Ti alloy have been investigated using high-pressure die casting. Solidification commences with the formation of primary α-Al phase in the shot sleeve and is completed in the die cavity. The average size of dendrites and fragmented dendrites of the primary α-Al phase formed in the shot sleeve is 43 μm, and the globular primary α-Al grains formed inside the die cavity is at a size of 7.5 μm. Solidification inside the die cavity also forms the lamellar Al-Mg2Si eutectic phase and the Fe-rich intermetallics. The size of the eutectic cells is about 10 μm, in which the lamellar α-Al phase is 0.41 μm thick. The Fe-rich intermetallic compound exhibits a compact morphology and is less than 2 μm with a composition of 1.62 at. pct Si, 3.94 at. pct Fe, and 2.31 at. pct Mn. A solute-enriched circular band is always observed parallel to the surface of the casting. The band zone separates the outer skin region from the central region of the casting. The solute concentration is consistent in the skin region and shows a general drop toward the center inside the band for Mg and Si. The peak of the solute enrichment in the band zone is much higher than the nominal composition of the alloy. The die casting exhibits a combination of brittle and ductile fracture. There is no significant difference on the fracture morphology in the three regions. The band zone is not significantly detrimental in terms of the fracture mechanism in the die casting. Calculations using the Mullins and Sekerka stability criterion reveal that the solidification of the primary α-Al phase inside the die cavity has been completed before the spherical α-Al globules begin to lose their stability, but the α-Al grains formed in the shot sleeve exceed the limit of spherical growth and therefore exhibit a dendritic morphology. 相似文献
2.
Troy D. Topping Byungmin Ahn Ying Li Steven R. Nutt Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2012,43(2):505-519
Aluminum alloys with nanocrystalline (NC) and ultrafine grain (UFG) size are of interest because of their strengths that are
typically 30 pct greater than conventionally processed alloys of the same composition. In this study, UFG AA 5083 plate was
prepared by quasi-isostatic (QI) forging of cryomilled powder, and the microstructure and mechanical behavior was investigated
and compared with the behavior of coarse-grained AA 5083. Forging parameters were adjusted in an effort to strengthen the
UFG material while retaining some tensile ductility. Different forging parameters were employed on three plates, with approximate
dimensions of 254 mm diameter and 19 mm thickness. The overarching goal of the current effort was to increase strength through
minimized grain growth during processing while maintaining ductility by breaking up prior particle boundaries (PPBs) with
high forging pressures. Mechanical tests revealed that strength increased inversely with grain size, whereas ductility for
some of the experimental materials was preserved at the level of the conventional alloy. The application of the Hall-Petch
relationship to the materials was studied and is discussed in detail with consideration given to strengthening mechanisms
other than grain size, including dispersion (Orowan), solid solution, and dislocation strengthening. 相似文献
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4.
Influence of Solidification Thermal Parameters on the Columnar-to-Equiaxed Transition of Aluminum-Zinc and Zinc-Aluminum Alloys 总被引:1,自引:0,他引:1
Understanding the interaction between the parameters involved in the columnar-to-equiaxed transition (CET) has gained considerable
attention over the last two decades in the study of the structure of ingot castings. The present investigation was undertaken
to investigate experimentally the directional solidification of Al-Zn and Zn-Al (ZA) alloys under different conditions of
superheat and heat-transfer efficiencies at the metal/mold interface. The CET is observed; grain sizes are measured and the
observations are related to the solidification thermal parameters: cooling rates, growth rates, thermal gradients, and recalescence
determined from the temperature vs time curves. The temperature gradient in the melt, measured during the transition, is between –0.338 °C/mm and 0.167 °C/mm.
In addition, there is an increase in the velocity of the liquidus front faster than the solidus front, which increases the
size of the mushy zone. The size of the equiaxed grains increases with distance from the transition, an observation that was
independent of alloy composition. The observations indicate that the transition is the result of a competition between coarse
columnar dendrites and finer equiaxed dendrites. The results are compared with those previously obtained in lead-tin alloys.
This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation:
in Honor of Prof. John Hunt,” which occurred March 13–15, 2006 during the TMS Spring Meeting in San Antonio, Texas, under
the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee. 相似文献
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6.
Basudev Bhattacharya 《Metallurgical and Materials Transactions A》2012,43(6):1747-1759
The microstructural changes in a 0.05C-26.3Mn-4.88Si-4.13Al-Fe alloy were studied. The two constituting phases were austenite and ordered DO3. The morphology of austenite phase was found to be different under various conditions. The DO3 phase had a modulated microstructure, and secondary austenite flakes precipitated within the DO3 matrix when both cast and hot-rolled alloys were heat treated at 1073 K (800 °C). An attempt was made to explain the secondary austenite precipitation in view of a schematic phase diagram. 相似文献
7.
采用液态压铸技术,研究了压铸工艺参数对AM60B合金组织缺陷的影响。试验结果表明,当浇注温度为680℃、模具温度为180℃、压射速度为3.0m/s、压射比压为75MPa时,压铸镁合金AM60B可以获得组织均匀细小、表面光滑、缺陷极少的铸件。 相似文献
8.
《Canadian Metallurgical Quarterly》2013,52(3-4):169-177
AbstractIn modeling the solidification of an alloy, two central numerical problems are:<list list-type="order"><list-item>The calculation of thermal and species transport fields which satisfy the conservation equations and are also consistent with the underlying thermodynamics.</list-item><list-item>The treatment of local scale solute diffusion.</list-item></list>In this paper, in the context of modeling inverse segregation in a uni-directionally solidified casting, a recently proposed implicit/explicit time integration scheme for coupling thermal and solutal fields is presented and possible ways of capturing the local scale solute diffusion in a macroscopic model are explored. A key element in this work is the validation of the proposed approach by comparison with a sophisticated similarity solution. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved. Résumé Lors de la modélisation de la solidification d'un alliage, on trouve deux problèmes numeriques centraux:<list list-type="order"><list-item>Le calcul de champs de transort thermique et de transport des èspeces qui satisfont les équations de conservation et qui sont aussi consistants avec la thermodynamic sous-jacente.</list-item><list-item>Le traitement de la diffusion de soluté à l'échelle locale.</list-item></list>Dans cet article, dans le contexte de modélisation de la ségrégation inverse d'un moulage à proposé récemment pour le couplage des champs thermiques et de soluté. On explore également des facons possibles de capturer, dans un modèle macroscopique, la diffusion de soluté à l'échelle locale. La validation de l'approche proposee en comparaison avec une solution sophistiquee de similarite constitue un element cle de ce travail. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved. 相似文献
9.
Kesheng Zuo Haitao Zhang Ke Qin Jianzhong Cui Qingzhang Chen 《Metallurgical and Materials Transactions B》2017,48(4):1981-1991
The effects of process parameters on the solidification structure of A390 aluminum alloy hollow billets prepared by direct-chill casting were investigated. The decrease of casting temperature deteriorated the homogeneity and increased the size of primary Si particles in the hollow billet. Although the average size of primary Si particles was not obviously affected by the increase of casting speed, the thickness of Si-depleted layer at the inner wall increased with the higher casting speed. The tensile strength of A390 alloy is a function of the percentage of coarse Si particles (larger than 35 μm) and the average size of primary Si particles. Higher and more stable tensile strength can be received in the hollow billet with the casting temperature of 1050 K (777 °C), because the fine and uniformly distributed primary Si particles were obtained in the hollow billet. 相似文献
10.
Influence of Rare Earths on the Directional Solidification Microstructure of Tin-Lead Eutectic Alloy
InfluenceofRareEarthsontheDirectionalSolidificationMicrostructureofTinLeadEutecticAloyZhuYing(朱颖),FangHongyuan(方洪渊),QianYiyu... 相似文献
11.
J.B. Jordon M.F. Horstemeyer N. Yang J.F. Major K.A. Gall J. Fan D.L. McDowell 《Metallurgical and Materials Transactions A》2010,41(2):356-363
We examine the dependence of fatigue properties on the different size scale microstructural inclusions of a cast A356 aluminum
alloy in order to quantify the structure-property relations. Scanning electron microscopy (SEM) analysis was performed on
fatigue specimens that included three different dendrite cell sizes (DCSs). Where past studies have focused upon DCSs or pore
size effects on fatigue life, this study includes other metrics such as nearest neighbor distance (NND) of inclusions, inclusion
distance to the free surface, and inclusion type (porosity or oxides). The present study is necessary to separate the effects
of numerous microstructural inclusions that have a confounding effect on the fatigue life. The results clearly showed that
the maximum pore size (MPS), NND of gas pores, and DCS all can influence the fatigue life. These conclusions are presumed
to be typical of other cast alloys with similar second-phase constituents and inclusions. As such, the inclusion-property
relations of this work were employed in a microstructure-based fatigue model operating on the crack incubation and MSC with
good results. 相似文献
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Laurentiu Nastac 《Metallurgical and Materials Transactions B》2014,45(1):44-50
This paper describes the development and validation of a comprehensive multiscale modeling approach capable of predicting at the mesoscopic scale level the ingot solidification structure and solidification-related defects commonly occurring during the vacuum arc remelting (VAR) process. The approach consists of a coupling between a fully transient macroscopic code and a mesoscopic solidification structure code. The predictions from the multiscale model, including grain morphology and size and columnar-to-equiaxed transition, were validated against experimental measurements for a 20-inch (508 mm) diameter VAR alloy 718 ingots. The validated model was then used to investigate the effects of melting rate and ingot diameter on the solidification structure of VAR processed 718 ingots. 相似文献
14.
Influence of Solute Content and Solidification Parameters on Grain Refinement of Aluminum Weld Metal
Philipp Schempp Carl Edward Cross Andreas Pittner Michael Rethmeier 《Metallurgical and Materials Transactions A》2013,44(7):3198-3210
Grain refinement provides an important possibility to enhance the mechanical properties (e.g., strength and ductility) and the weldability (susceptibility to solidification cracking) of aluminum weld metal. In the current study, a filler metal consisting of aluminum base metal and different amounts of commercial grain refiner Al Ti5B1 was produced. The filler metal was then deposited in the base metal and fused in a GTA welding process. Additions of titanium and boron reduced the weld metal mean grain size considerably and resulted in a transition from columnar to equiaxed grain shape (CET). In commercial pure aluminum (Alloy 1050A), the grain-refining efficiency was higher than that in the Al alloys 6082 and 5083. Different welding and solidification parameters influenced the grain size response only slightly. Furthermore, the observed grain-size reduction was analyzed by means of the undercooling parameter P and the growth restriction parameter Q, which revealed the influence of solute elements and nucleant particles on grain size. 相似文献
15.
A. Gautam Revankar P. Chakravarthy R. Arockia Kumar 《Transactions of the Indian Institute of Metals》2017,70(3):623-630
It is well known that the kinetics of precipitation is altered with the degree of cold working and this study aims to bring out the effect of cold working on the aging response of the alloy AA6061 along with the studies of microstructural evolution. The as-received samples were initially solutionized at 530 °C and subsequently aged at 160 °C for varying time from 2 to 28 h at intervals of 2 h. A peak hardness of 124 HV was observed at 15 h beyond which the hardness decreased due to overaging. The solutionized samples were also subjected to various degrees of cold working and the increase in hardness by virtue of strain hardening was observed. The samples that were cold worked to various levels (10, 20, 30% etc.) were subsequently aged at 160 °C for 4 h. A peak hardness of 134 HV was obtained for the sample cold worked to 75% and subsequently aged for 4 h and this was attributed to the increase in the dislocation density that improved the kinetics of precipitation. The evolution of microstructure for various samples during the course of aging was observed using transmission electron microscopy and the changes in the properties were correlated to the obtained microstructure. 相似文献
16.
The heat flow model previously developed for a pure metal is extended to the solidification of an alloy over a range of temperatures.
The equations are then applied to rapid surface melting and solidification of an alloy substrate. The substrate is subjected
to a pulse of stationary high intensity heat flux over a circular region on its bounding surface. The finite difference form
of the heat transfer equation is written in terms of dimensionless nodal temperature and enthalpy in an oblate spheroidal
coordinate system. A numerical solution technique is developed for an alloy which precipitates a eutectic at the end of solidification.
Generalized solutions are presented for an Al-4.5 wt pct Cu alloy subjected to a uniform heat flux distribution over the circular
region. Dimensionless temperature distributions, size and location of the “mushy” zone, and average cooling rate during solidification
are calculated as a function of the product of absorbed heat flux,q, the radius of the circular region, a, and time. General trends established show that for a given product ofqa all isotherms are located at the same dimensionless distance for identical Fourier numbers. The results show that loss of
superheat and shallower temperature gradients during solidification result in significantly larger “mushy” zone sizes than
during melting. Furthermore, for a given set of process parameters, the average cooling rate increases with distance solidified
from the bottom to the top of the melt pool. 相似文献
17.
W. J. Boettinger L. A. Bendersky R. J. Schaefer F. S. Biancaniello 《Metallurgical and Materials Transactions A》1988,19(4):1101-1107
Examination of the effect of rapid solidification velocity on the microstructure of Al-3.7 wt pct Ni-1.5 wt pct Fe has revealed
a new mechanism for the formation of discrete second phase particles in rapidly solidified alloys. Cellular growth of α-Al
occurs with the intercellular phase, Al9(Fe, Ni2 in two distinct morphologies. At low velocity (<50 cm/sec) the phase is continuous in the growth direction while at higher
velocity discrete rounded particles are observed. Analysis of the orientation relationship and the number of variants which
exists between phases leads to the proposal of a mechanism where liquid droplets are deposited by the grooves of a moving
cellular interface. These droplets solidify subsequently to form the rounded second phase particles. 相似文献
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19.
Zhang Xubin Chen Wei Ren Ying Zhang Lifeng 《Metallurgical and Materials Transactions B》2019,50(3):1444-1460
Metallurgical and Materials Transactions B - In the current study, the two-dimensional mold model was applied to investigate the influence of different casting parameters on the initial... 相似文献